Indraprastha, the original city of Delhi was supposed to be constructed where now exists the Purana Qila. The Afghan ruler, Sher Shah, who briefly interrupted the Mughal Empire by defeating Humayun, completed the fort during his reign from 1538-45.
Pandavas had built their capital, Indraprastha at the place where the old fort stands today. This fort, now in ruins, was the seat for administration for many emperors. The legendary Prithviraj Chauhan ruled from here till he was defeated by Abdali in the battle of Panipat.
The fort is located south-east of the India Gate and north of Humayun’s Tomb and the Nizamuddin railway station. It has massive walls and three large gateways. There is a small octagonal red sandstone tower, the Sher Mandal, in side the fort near the South gate. It was later used by Humayun as a library. While descending the stairs of this tower one day in 1556, Humayun slipped, fell and received injuries from which he later died. The Qila-i-Kuhran Mosque, or Mosque of Sher Shah, lies just beyond it and is in a fairly reasonable condition.
A nice place to visit while visiting Delhi. In evening you will find the place very appealing. You can see the transformation of Delhi from the ramparts of the Qila. There is a small archaeological museum just inside the main gate. A new light & sound show is held by the Department of Delhi Tourism every evening. Timings and Tickets are available from the tourist office.